Hydraulic machines, for example hydraulic earthworking machines such as loaders, dozers, graders, and the like, are commonly used to perform work operations which require large amounts of power. The characteristics of hydraulic systems provide the power needed for the machines to function productively and efficiently.
However, there are characteristics of hydraulic systems which are not desired. For example, flow ripple caused by the geometry, port timing, and speed of hydraulic pumps and motors creates pressure waves which in turn generate noise in the systems. This noise can be a distraction and a nuisance to an operator responsible for controlling the machine for long periods of time.
Historically, attempts have been made to reduce the amount of noise by enclosing hydraulic systems in acoustic enclosures. However, this leads to extra expense in designing and building the hydraulic machine, and makes routine maintenance more difficult. In addition, it is not feasible to enclose the entire hydraulic system, since the hydraulics of a machine are generally disposed throughout the machine. Furthermore, acoustic enclosures can only muffle the noise and do nothing to reduce the noise itself.
In commonly-owned U.S. Pat. No. 5,560,205, Huebner discloses a system which uses a fluid vessel having a volumetric space of a predetermined size located in the hydraulic system generally adjacent a pump, and a flow restrictor located in the system downstream of the fluid vessel. The flow restrictor, preferably, is variable to provide fluid noise reduction over a wide range of pressures and flow rates, and is externally controlled. However, an externally controlled, variable area flow restrictor can add significant cost and complexity to a hydraulic system, and therefore may not always be the desired solution for hydraulic noise problems.
It is known in the art to use pressure reducing valves for various reasons. In addition, pressure reducing valves, by nature of their ability to reduce pressure in a hydraulic system, are also known to reduce hydraulic noise caused by flow ripple. However, pressure reducing valves are typically used for applications such as pressure regulating, fixed pressure reduction, and the like. A pressure reducing valve used specifically for hydraulic fluid noise reduction would preferably result in the input pressure being a desired small percentage higher than the output pressure. The valve would maintain the same percentage difference for all pressures and flow rates. In addition, a pressure reducing valve for the express purpose of fluid noise reduction would preferably be of relatively simple design and be economical.
The present invention is directed to overcoming one or more of the problems as set forth above.